This invention relates to a method of producing a high strength fiber and to a high strength polyethylene fiber so produced.
For various uses, fibers having higher than usual strength are required. For example, the fibers used in fiber reinforced articles, and load bearing devices such as ropes, etc., should be strong. Typically the fibers used are of glass, carbon, steel or the like. For some uses it is desirable that the fiber also have the ability to deform or elongate. Polymeric fibers have the desirable elongation, however, commercially available, polymeric fibers generally have insufficient strength for many uses.
Various processes have been proposed in the art to improve the strength of polymeric fibers. One such process is a gel crystallization technique, another is solid state extrusion. These processes while they do provide polymeric fibers of improved strength are undesirably slow. Further, the fibers exhibit low elongation and are subject to irreversible creep when subjected to high forces.
Crosslinking of polymeric fibers by irradiation has been proposed. It ha been found that if polymeric fibers are stretched to increase their strength by orientation and then irradiated the physical properties of the polymer tend to degrade. There are reports in the literature of crosslinking the polymeric material of the fibers before stretching. However, the technique employed in the prior art resulted only in a relatively modest improvement in the strength of the fibers.
This invention provides a method of producing high strength polymeric fibers having unique properties. The resulting fibers can be used for making fabrics and articles such as garments, and for producing reinforced articles such as fiber reinforced composites and the like. Further the fibers are heat-shrinkable, that is, on application of heat, generally to a temperature of about T.sub.1 (as herein defined), the fibers shrink toward their undrawn dimension. The fibers thus can be used to produce heat-shrinkable articles and composites.